Health officials have identified more cases of the coronavirus on the cruise ship that is in limbo off the coast of San Francisco. And elsewhere around the country, states are reporting more cases as health officials ramp up testing. Joining us with the latest is NPR's science correspondent Richard Harris.

Welcome to the studio.

RICHARD HARRIS, BYLINE: Thanks, Audie.

CORNISH: Let's start with that cruise ship. What's the situation at this point?

HARRIS: Well, of the thousands of people on the ship, they've tested 46. And of those, we learned today, 21 are infected with the coronavirus. Nineteen of those are crew members, and you'll recall that the virus has been circulating on that ship for some time. It was discovered when a passenger who returned home to California died earlier this week.

CORNISH: What more are they going to do with the people on the ship?

HARRIS: Well, President Trump, earlier today, said he would prefer the ship to remain offshore so the number of cases in this country wouldn't increase. But he said, I'll leave the decision to Vice President Mike Pence and the task force. And the task force working with California's Gov. Newsom have decided to bring the ship ashore to a port that's not used for passengers. Here's Vice President Pence.

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VICE PRESIDENT MIKE PENCE: All passengers and crew will be tested for the coronavirus. Those that need to be quarantined will be quarantined. Those that require additional medical attention will receive it.

HARRIS: He later spoke of military bases as possible destinations. That's happened with the previous cruise ship passengers, you'll recall. And he said the same precautions would be used to assure the public that they are not at risk from these people.

CORNISH: How long will it take to test everyone aboard?

HARRIS: Members of the task force didn't say. All week, the administration has been stressing that test kits are being churned out, and they have the capacity to test hundreds of thousands of samples. But, you know, they have not addressed the real bottleneck here, which is that labs are not set up to do testing on that scale. They're moving in that direction, but it won't happen right away. Now, some of that pressure will be relieved by the big testing companies Quest and LabCorp, which have developed a testing protocol. And they're ramping up right now. Pence spoke about that in the White House briefing.

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PENCE: We trust in a matter of weeks, the coronavirus tests will be broadly available to the public and available to any American that is symptomatic and has a concern about the possibility of having contracted the coronavirus.

HARRIS: Now, that's a step forward, but those test results won't come back for several days. So if you're a doctor with a more urgent case, you'll probably still want to rely on your local health labs or the local universities that have created their own tests.

CORNISH: At this point, I know more than 20 states have reported some cases. That's raising anxiety around the country. We just heard about South by Southwest - the music festival in Texas - being canceled this afternoon. What advice is the task force offering about travel, about gatherings?

HARRIS: Well, they focused this evening on the most vulnerable people. That is people with underlying health conditions and serious ones at that, such as congestive heart failure, diabetes or serious lung disease. Dr. Anthony Fauci from the National Institutes of Health said those at highest risk are elderly people with serious underlying health conditions, and Pence underscored that point.

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PENCE: It is a good time for any American who is elderly by however they define it and has a serious underlying health condition to think carefully about travel.

HARRIS: That includes plane trips as well as cruise ships. And, you know, it is - it's a tough call for the administration to be saying this because they want people to continue to spend money. They are concerned about where the economy is heading. But at the same time, they recognize that these health risks are really real for these individuals. That said, Vice President Pence is heading to Florida for the weekend to talk to executives in the cruise ship industry; one of the industries that is, obviously, going to be hit hardest by this.